EP0287661A1

EP0287661A1 - Scan controller for nmr imaging apparatus

Info

Publication number: EP0287661A1
Application number: EP87901112A
Authority: EP
Inventors: Toru Yokogawa Medical Systems Ltd. Shimazaki
Original assignee: Yokogawa Medical Systems Ltd
Current assignee: GE Healthcare Japan Corp
Priority date: 1986-01-29
Filing date: 1987-01-28
Publication date: 1988-10-26
Also published as: WO1987004608A1; JPS62176442A; US4954780A; EP0287661A4

Abstract

A scan controller for NMR imaging apparatus which stores control signals having high amplitude resolution for a variety of sequences using small amounts of memory, and which easily assembles any sequence. The waveforms of the control signals are stored in a waveform memory (101) while the amplitude thereof are stored in an amplitude memory (102) in the order of events in the sequence, and the duration designating values thereof are stored in a time memory (103) in the order of events in the sequence. The waveform memory (101) is read by an address counter (104) which operates on clocks determined by values read from the time memory (103), and the output thereof is converted through a first D/A converter (105) into an analog signal and is produced. At this moment, the amplitude of the output signal of the first D/A converter (105) is determined by applying a stored amplitude read from the amplitude memory (102) for every event as a fullscale value to the first D/A converter (105) through a second D/A converter (106).

Description

(Technical Field)

This invention is related to an improved scan controller for imaging devices that acquire tomographic images of a subject by using nuclear magnetic resonance. In other words, this invention is related to the scan controller for NMR imaging devices with improved memory performance for scan control signals.

(Background Art)

The NMR imaging device has a magnet assembly that includes a static magnetic field coil to generate a uniform static magnetic field, and a gradient magnetic field coil that generates straight and gradient magnetic fields (in the same magnetic field as the static magnetic field) in the X, Y; and Z directions. Also included are transmitting and receiving sections that detect NMR signals from the subject by applying a high-frequency pulse (RF electromagnetic wave) to the magnetic field generated by the magnetic assembly, and a control and image processing section that controls the transmitting/receiving sections and magnetic assembly, and processes the detected data for image display. When controlled by the control and image processing section, this NMR imaging device sequentially outputs high-frequency pulses based on the Saturation Recovery method or Inversion Recovery method. The control and image processing sections also control the magnet assembly and transmitting/receiving sections to restore images through sequential data collection based on Fourier analysis, for example.
The control and image processing section is equipped with a scan controller. The scan controller generates a gradient magnetic field and high-frequency pulse according to the respective operation sequences of the magnet assembly and transmitting/receiving sections. Control signals used to generate the gradient magnetic field and high-frequency pulse according to sequence are stored in advance, and are read to execute the sequence. Stored control signals have different waveforms, amplitudes, and continuation times according to the type of sequence. Therefore, the scan controller requires large memory capacity to store consecutive control signals. Furthermore, to enhance the resolution of the control signal amplitude, digital data uses a number of bits to express the amplitude. This in turn increases the use of memory.

(Disclosure of Invention)

An object of this invention is to provide a scan controller for NMR imaging devices that can store control signals of high-amplitude resolution for various sequences using a small memory capacity.
Another object of the invention is to provide a scan controller for NMR imaging devices that can randomly assemble sequences.
The scan controller related to this invention stores the waveforms of control signals in waveform memory 101. The controller also stores the amplitudes of control signals in amplitude memory 102, and stores the specified continuation time value of control signals in time memory 103 in order of sequence events.
The scan controller reads waveform memory 101 by using address counter 104, which operates based on a clock determined by the value read from time memory 103. The scan controller converts the output into an analog signal by using the first D/A converter 105. The amplitute of the signal output from the first D/A converter 105 is determined by assigning it the memory value of the amplitude read from amplitude memory 102 for individual events (through the second D/A converter 106) as the full-scale value.

(Brief Description of Drawings)

Figure 1 is a block diagram of the NMR imaging device for which the scan controller of this invention is used.
Figure 2 is a block diagram that shows the embodiment of this invention.
Fig. 3 is a pulse sequence that shows an example of operating the NMR imaging device shown in Fig. 1.

(Best Mode for Carrying out the Invention)

Turning now to the drawings, Fig. 1 is a block diagram showing the embodiment of this invention. Magnet assembly 1 has an internal space section for inserting the subject. This space section is surrounded by a static magnetic field coil that applies a fixed static magnetic field to the subject, X, Y, and Z gradient magnetic field coils to generate gradient magnetic fields, an RF transmitting coil to provinde high-frequency pulses for exciting nuclear spin inside the subject, and a receiving coil to detect NMR signals from the subject (Fig. omitted). The static magentic field coil, gradient magnetic field coils, RF transmitting coil, and receiving coil are respectively connected to main magnetic field power supply 2, gradient magnetic field drive circuit 3, RF power amplifier 4, and pre-amplifier 5. Sequence storage circuit 10 operates gradient magnetic field drive circuit 3, gate modulation circuit 6 and A/D converter 11 according to instructions issued from computer 13 in the preset sequence. Phase detector 8 refers to the output from RF oscillation circuit 7 as a signal, then provides A/D converter 11 with the NMR signal that is detected by the receiving coil and sent via pre-amplifier 5 after phase detection. A/D converter 11 inputs the NMR signal provided by phase detector 8 after analog-to-digital conversion to computer 13. Computer 13 exchanges data between operating console 12, and switches the operation of sequence storage circuit 10 or reloads its memory to set various scan sequences. Computer 13 uses the data sent from A/D converter 11 to execute the carries out operations for reconfiguring the distribution of information on resonance energy into images, and outputs this reconfigured image data to display unit 9.
Sequence storage circuit 10 contains the scan controller of this invention (described later), and executes scanning in the sequence shown in Fig. 3 through scan controller operation. Figure. 3 is a waveform diagram of data collection through scanning according to Fourier's pulse sequence (RF denotes a high-frequency pulse; G_x, Gy, and G_z indicate gradient magnetic fields). The gradient magnetic field functions are divided into G_x for the'readout gradient, Gy for the warp gradient, and G_z for the slice positioning gradient. The NMR signal shows the FID signal after a 90° pulse, and the Spin Echo signal (SE signal) after a 120° pulse.
The sequence is divided by events that generate individual pulses that are numbered. In Event 1, spins in the slice surfaces vertical to axis z (centered at z=0) are excited by a 90° pulse and gradient magnetic field G_z ⁺.
The envelope of the 90° pulse is used for the sine-wave function, for example. In Event 2, Gx+, Gy_n, and G_z ^- are applied. Gy_n shifts the phase of the spin in proportion to the directional position of y through an operation called a warp, while the strength of such operation is controlled to be different for each view. In Event 3, a 180° pulse is applied. The envelope of this 180° pulse is also used for the function, for example. In Event 4, the SE signal is measured while applying gradient magnetic field G_x ⁺.
As described thus far, a high-frequency pulse and gradient magnetic field are generated for each event according to the control signals of specific waveforms. The control signals of these waveforms, for example, are generated by the scan controller as shown in Fig. 2. In Fig. 2, 101 is the waveform memory storing the control signal waveform. The memory consists of four sets: one for each of the RF, G_xf Gy_n, and G_z waveforms. Figure 2 shows the waveform memory for RF as a typical example. The RF pulse envelope for one event is written to waveform memory 101 as a waveform consisting of N steps. The values of individual waveform steps stored in waveform memory 101 are sequentially read according to the address specified by address counter 104. Address counter 104 is provided in four sets corresponding to the four sets of waveform memory 101. Figure 2 only shows one of them. Digital data read from waveform memory 101 is converted into an analog signal by the first D/A converter 105 for output as the control signal.
Amplitude memory 102 stores the amplitudes of control signals stored in waveform memory 101 (in the order of events) in the form of multiplicance. The multiplying factor of amplitude includes zero and a negative value. Amplitude memory 102 is also provided in four sets corresponding to the four sets of waveform memory. Figure 2 only shows one of them. Digital data read from amplitude memory 102 is converted into an analog signal by the second D/A converter 106 for application to the first D/A converter 105 for its full-scale setting value. Consequently, the value of the output signal from the first D/A converter 105 becomes equal to the product of multiplying the storage value of waveform memory 101 by the corresponding value of amplitude memory 102. These two storage values may be multiplied by each other in the digital signal stage for subsequent conversion into an analog signal.
Time memory 103 stores the data that defines the time axis length of one waveform stored in waveform memory 101 or the continuation time of the control signal for one event (in order of events). Time memory 103 also consists of four sets that correspond to those of four-set waveform memory 101. In Fig. 2, time memory 103 stores the data during the cycle of the clock signal input to address counter 104. A short clock cycle is stored for the control signal of a short continuation time, while a long clock cycle is stored for one with a long continuation time.
Waveform memory 101, amplitude memory 102, and time memory 103 are connected to'CPU131 and memory 132 inside computer 13 by data bus 133, and are controlled by CPU131. Consequently, the contents of these memories can be reloaded by CPU131. Storage data in amplitude memory 102 and time memory 103 are simultaneously read by a common event number provided by CPU131. Event number is incremented by one when an event is terminated.
For this type of scan controller, four sets of waveform memory 101 each store the waveform for one event for RF, G_x, Gy_n, and G_z to be used in the sequence sho.wn in Figr. 3. The four sets of amplitude memory 102 store the amplitude multiplying factors for the events of individual signals. Time memory 103 stores the clock cycle read from respective waveform memories for individual events. Thus, the sequence shown in Fig. 3 is executed by CPU131, while it consecutively updates the event number at a specific timing. The scan controller for this invention has the following characteristics:
The amplitude and continuation time of control signals are respectively stored in amplitude memory 102 and time memory 103. Therefore, the control signal to be stored in waveform memory 101 may be one type, regardless of the amplitude and continuation time or number of events, (as long as the waveform is the same). This can largely reduce the number of memories used to store control signals. Because the control signal will be the product of the storage value of waveform memory 101 multiplied by the storage value of amplitude memory 103, the number of control signal bits will be the sum of the bits of both storage values. Therefore, a control output of high-amplitude resolution can be obtained without increasing the number of bits for the storage value of waveform memory 101. If executing an other sequence using the same waveform, only the contents of amplitude memory 102 and time memory 103 should'be reloaded. If executing a sequence using an other waveform, the waveform of waveform memory 101 should be reloaded or the required waveform should be selected from the preloaded waveforms. Therefore, sequences can be randomly and easily assembled.
The ideal mode for the embodiment of this invention is illustrative and not restrictive, and the scope of the invention indicated by appended claims and all variations within the meaning of such claims can be easily determined by those possessing knowledge in the technical fields to which this invention applies.

Claims

1. A scan controller has been developed for NMR imaging devices, to control high-frequency pulses and/or gradient magnetic fields in a pulse sequence for NMR imaging configured by a series of multiple events). It consits of the following:

waveform memory (101) to store control signal waveforms, amplitude memory (102) to store control signal amplituds in order of sequence events,

time memory (103) to store the specified values of control signal continuation times in order of sequence events,

amplitude memory and time memory (131) readout to read amplitude memory and time memory according to the order of events, waveform memory (104) readout being based on a clock determined by the value read from time memory, and the storage value read from waveform memory, and

the means to output the product of waveform memory and amplitude memory readout values (105 and 106).

2. Waveform memory readout is done by the scan controller for NMR imaging devices (as described in Item 1 of the present Claim) using an address counter for counting clocks.

3. Output is done by the scan controller for NMR imaging devices (as described in Item 1 of the present Claim) using the first D/A converter that converts the waveform memory readout value into an analog signal, and the second D/A converter that converts the amplitude memory readout value into an analog signal to become the full-scale setting value for the first D/A converter.

4. Output is done by the scan controller for NMR imaging devices (as described in Item 1 of the present Claim) by converting the product of the waveform memory and amplitude memory readout values into an analog signal.